Because of the usefulness as a coloring material, organic pigments have been used as a colored composition for an extremely wide range of applications such as offset ink, gravure ink, flexographic ink, plastic colorant, coating material, color toner, color filter resist ink for color filters, and inkjet ink. Depending on the intended application, these organic pigments are required to have coloring properties such as coloring strength, brightness and hue, durabilities such as lightfastness, heat resistance, acid resistance, alkali resistance, solvent resistance and migration resistance, and properties such as dispersibility and fluidity.
For these reasons, in order to adjust hue and to improve durability such as weather resistance, lightfastness, heat resistance and drug resistance, a halogenated organic pigment comprising halogen in the structure thereof has been frequently used. Examples of a representative halogenated organic pigment include a halogenated quinacridone pigment, C. I. Pigment Blue 15:1, C. I. Pigment Blue 15:2, C. I. Pigment Green 7, C. I. Pigment Green 36, C. I. Pigment Violet 23, C. I. Pigment Red 254, C. I. Pigment Yellow 138, C. I. Pigment Yellow 109, and C. I. Pigment Yellow 110 (Non Patent Literature 1).
The “halogenated quinacridone pigment” is a generic name for compounds, each of which has quino[2,3-b]acridine-7,14 (5H,12H)-dione as a basic structure, and some of hydrogen atoms of which are substituted with halogen atoms. As described in Non Patent Literature 1, as examples of such a halogenated quinacridone pigment, 2,9-dichloroquinacridone and 3,10-dichloroquinacridone are registered as C. I. Pigment Red 202 and C. I. Pigment Red 209, respectively, in the database of Color Index International. In addition, a solid solution of unsubstituted quinacridone and 4,11-dichloroquinacridone is registered and disclosed as C. I. Pigment Red 207.
Moreover, as halogenated quinacridones other than the above-mentioned halogenated quinacridone pigments, 3,10-dichloroquinacridone sodium sulfonate and phthalimidomethylated 3,10-dichloroquinacridone are disclosed in Patent Literature 1, and this publication describes that these halogenated quinacridone pigments are used as pigment dispersion aid in inks for ink jetting.
As quinacridone compounds other than these halogenated quinacridones, an unsubstituted quinacridone that is quino[2,3-b]acridine-7,14 (5H,12H)-dione itself, and 2,9-dimethylquinacridone in which two methyl groups are substituted are known as C. I. Pigment Violet 19 and C. I. Pigment Red 122, respectively. Moreover, Patent Literature 2 discloses a quinacridone in which a phthalimidomethyl group is substituted; Patent Literature 3 discloses a quinacridone in which a sulfonic acid group is substituted; and Patent Literature 4 discloses a quinacridone in which a —SO2NH—(CH2)3—N(C2H5)2 group is substituted.
The basic structure of quino[2,3-b]acridine-7,14 (5H,12H)-dione possessed by the quinacridone compound is a comparatively simple chemical structure. Thus, for using such a quinacridone compound as a pigment, there have been essential problems in that the adjustable range of color tone is narrow, and in that it is difficult to prepare fine particles because of its good crystallinity. However, as the aforementioned C. I. Pigment Red 207, many types of solid solution pigments have been found in which two or more types of quinacridones, which comprise dichloroquinacridone as a main body, are homogeneously mixed with one another. As a result, the range of color tone has been widened, and at the same time, it has become easier to prepare fine pigment particles because crystallinity has been reduced due to being a mixture, and it has started to be used for applications requiring extremely fine particles such as color toner, inkjet ink, and color filter resist ink. Furthermore, in regards to quinacridones used as pigment dispersion aid, many types of halogenated quinacridones that are prepared by introducing a phthalimidomethyl group or a sulfonic acid group into a dichloroquinacridone have also been found as described above.
As mentioned above, a halogenated quinacridone, into which one or more halogen atoms are introduced, has become more and more of an industrially important compound. Under such circumstances, problems regarding their production have drawn attention. For example, a chloroaniline used as a starting raw material for production of a chlorinated quinacridone has been problematic regarding safety because it is suspected to be carcinogenic. This chlorinated quinacridone is comparatively expensive as an industrial chemical, and is scarcely available. Moreover, when a chlorinated quinacridone is produced using such a chloroaniline as a starting raw material, there is a problem with productivity in that a total yield becomes low in comparison to the case of producing an unsubstituted quinacridone using aniline as a starting raw material.
Furthermore, chlorinated quinacridones that are industrially produced are substantially only a dichloroquinacridone and a solid solution thereof. When they are used in a colored composition for an ink, a coating material, a plastic material, color toner, inkjet ink, or color filter resist ink, etc., there are problems in that the adjustable range of color tone is still narrow, and it is difficult to prepare into fine particles.
The above-described halogenated organic pigment comprising a halogenated quinacridone can be produced by various methods. Those methods can be broadly categorized into production methods in which an organic pigment serving as a mother material is halogenated with a halogenating agent, and production methods in which a raw material having a halogen atom is used. In the case of the latter method, in general, such a raw material having a halogen atom is scarcely available and is expensive in many cases. Moreover, since the obtained halogenated organic pigment is a single compound, it is difficult to adjust hue and the like by controlling the number of halogen substitutions in the pigment, and thus in many cases, a halogenated organic pigment having excellent coloring properties cannot be obtained. Therefore, in general, the former methods are adopted in the industrial field.
As the former methods, (1) a method of halogenating an organic pigment using chlorine or bromine as a halogenating agent (e.g., Patent Literature 5), (2) a method of halogenating an organic pigment using N-bromosuccinimide as a halogenating agent (e.g., Patent Literature 6), and the like are known.
However, in the case of the method described in (1) above, since highly toxic chlorine or bromine is used, safety-conscious, large-scale special production equipment is required. In addition, equipment for treating a large amount of hydrogen halide gas generated as a by-product is also required. Furthermore, there has been a problem in that, due to metal elements (iron, aluminum, calcium, etc.) that have been mixed during a step of producing a pigment (in production equipment, a reaction solvent, etc.), by-products and unfavorable impurities are generated as a result of substitution or laking of a portion of a desired halogenated organic pigment with the metal elements, and are mixed into the obtained halogenated organic pigment, which adversely affect properties required for intended applications.
On the other hand, succinimide is generated as a by-product in the method described in (2) above. Thus, there have been problems such that it requires equipment for separating and removing the succinimide from the obtained halogenated organic pigment and then treating it. In addition, this method has also been problematic in that environmentally unfavorable organic solvents, such as trifluoroacetic acid or chloroform, are used in many cases, and the yield of the halogenation reaction is poor.
Furthermore, in the conventional production methods, the obtained crude halogenated organic pigment has a large particle diameter in many cases, and tends to be poor in terms of coloring properties such as coloring strength or brightness. Hence, it is difficult to directly use such a crude halogenated organic pigment as a coloring material. Thus, in many cases, in order to process the crude halogenated organic pigment into a pigment form that is highly variable as a coloring material, a pigmentation step such as acid pasting is required after the crude halogenated organic pigment is produced. However, from the viewpoint of productivity, it has been a desire to develop a method for producing a halogenated organic pigment useful as a coloring material without performing such a pigmentation step.
Meanwhile, in the case of halogenation of a common organic compound, halogenation methods in which various halogenating agents other than the aforementioned agents are used have been known. However, differing from the properties of a common organic compound, an organic pigment has poor solubility in organic solvents. Thus, it is anticipated that the halogenation reaction will hardly progress under the same reaction conditions (a solvent, a halogenating agent, etc.) as those for the halogenation reaction of a common organic compound. Accordingly, it has been desired to develop a halogenating agent that can be preferably used in halogenation of an organic pigment and a method for producing a halogenated organic pigment using the same which can solve the aforementioned problem.